The consensus of opinion is your film has a fault - and well it might have. As suggested, a film test will quickly sort that out

However, two things give pause for thought

* You say the bluish tinge is in "some" of your pictures, which i take to mean not all of them

Check the prints: is the tinge only in those with open shade (?)

Our eyes see shade in tones of grey or black - whereas, in reality, shaded areas on a sunny day are blue and which your film will have faithfully recorded

A warming filter or day light balanced fill flash will eliminate that problem

* You start by saying the film is ISO 200 - then later it is 400

The difference between ISO 200 down to ISO 400 is 1 stop underexposure. Whilst colour negative film has enough latitude to handle the difference under normal conditions, depending on your (faulty?) exposure technique/combined with the wrong ISO setting on your camera, the film may have been underexposed by too much - giving a grainy, bluish result in "some of (your) pictures"

A blue cast in a color print is usually caused by ultra-violet light, but if you had a UV filter on the lens it shouldn't have happened. That is what a UV filter is for. It has to be the film or bad chemical balance at the lab. Get a reprint or two from the same negs at a different lab to see any difference.